1. Field of the Invention
The present invention is generally related to dipyridine-based compounds, and more particularly to dipyridine-based compounds and their use as electron-transporting and/or hole blocking materials or phosphorous host.
2. Description of the Prior Art
Organic light-emitting devices (OLEDs) have received much attention due to their potential applications to flat panel displays. OLEDs are generally composed of functionally divided organic multi-layers, e.g., hole transporting (HT), emissive, and electron transporting (ET) layers, and so on. In the last decade, many kinds of amorphous molecular semiconductor materials, working as HT materials and ET materials, have been proposed, and HT molecular semiconducting materials have become practical due to their high charge carrier mobility and excellent operational durability. On the other hand, there have been few reports of ET organic semiconducting amorphous materials with high performance (high-speed transportation of electrons, easy injection of electrons from the cathode, and good operational durability).
Efficient ET materials provide some advantages, such as lowering the operating voltage and power consumption. Moreover, if the ET materials have wide band gaps, in other words, deeper highest occupied molecular orbitals (HOMO), such ET materials can also work as hole blocking (HB) materials. The complete confinement of a hole in an emissive layer by the HB layer raises the quantum efficiencies of electroluminescence (EL). Oxadiazole is a well-known electron accepting component for building ET materials with high electron mobility, and oxadiazole derivatives (OXDs) exhibit wide band gap properties because oxadiazole restricts extensions of p-conjugation beyond the ring even if the molecule is co-planar. Accordingly, OXDs are a promising ET and HB material for OLEDs, but it has been widely accepted that OXDs should acquire durability capacity for long-term operations in OLEDs. Therefore, new electron-transporting and/or hole blocking materials are still needed corresponding to increasing thermal stability and practical operation durability.